Whenever I went to the mall, or this one coffee shop, and also at 7-11 outlets, I would get the notification "Sign in to wifi network", then I get redirected to their login page when trying to visit any webpage in my browser, I sign in, and I can connect after.

But I have been playing around with my android in the past month

installed AFWall+ to allow only Opera Mini to connect on 3G

installed ProxyDroid to view the traffic on one of my games (and to get infinite gold lol)

added Charles Proxy certificate

installed and uninstalled XPosed framework

other stuff

And I just recently realized, I never get the "Sign in to wifi network" notification anymore, and I just get a cannot connect error on the browser.

It seems my phone's ability to sign in to captive portals has been completely broken somewhere along the way. It used to work 100%, now NONE of the places work.